The very top rack, the Flex Tray, is completely plastic with a plastic foldable tray that sits atop it that your silverware/whatever goes on. All of the other racks are coated metal. When I say coated, they have a very durable paint-like coating, not like a plastic or rubber coating.
The Flex Tray and bottom rack are on normal rollers, while the center rack is on stainless steel ball bearings (so it rolls in and out incredibly quickly and smoothly).
Hope this helps.